In a known filling apparatus for fluid media (German Offenlegungsschrift No. 23 08 689), there is disclosed a dosing piston which is movable into an extended portion of the dosing cylinder where the outer surface of said piston is exposed. In this extended portion of the cylinder, the dosing piston becomes accessible for cleansing through a rinsing or cleaning medium. The rotary valve provided at the upper part of the dosing cylinder, however, cannot be made accessible in this known apparatus; thus it can neither be completely cleaned, nor, more importantly, can it be sterilized. For applications within the pharmaceutical industry in particular, such a filling apparatus, which cannot be rendered sterile, cannot be used. To meet this requirement for sterility, therefore, an apparatus is needed in which both the dosing piston and the rotary valve are fully accessible for cleansing via an enveloping fluid comprising a rinsing, cleaning, and/or sterilizing medium.